package map;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class L18 {
    public List<List<Integer>> fourSum(int[] nums, int target) {
        List<List<Integer>> result = new ArrayList<>();
        Arrays.sort(nums);
        for (int i=0;i<nums.length;i++){
            if (nums[i] > target && nums[i] >0){
                return result;
            }
            if (i>0 && nums[i]==nums[i-1]){
                continue;
            }
            for (int j=i+1;j<nums.length;j++){
                if (j>i+1 && nums[j]==nums[j-1]){
                    continue;
                }
                int left=j+1;
                int right= nums.length-1;
                while (left<right){
                    long sum = (long) nums[i] + nums[j] + nums[left] + nums[right];
                    if (sum>target){
                        right--;
                    } else if (sum<target){
                        left++;
                    }else {
                        result.add(Arrays.asList(nums[i],nums[j],nums[left],nums[right]));
                        while (left<right && nums[right]==nums[right-1]){
                            right--;//对c进行去重
                        }
                        while (left<right && nums[left]==nums[left+1]){
                            left++;//对d进行去重
                        }
                        right--;
                        left++;
                    }

                }

            }

        }
        return result;

    }
}
